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1990 C2 Heater Control Problem

Heating and Ventilation

Vehicle Information: Model: 911 -2; Year: 1990; Body Type: Convertible; Engine (type, size, modifications): Standard 6 cyc engine; Total Mileage: 100000;

I have been trying to get the heating system on this car to functioncorrectly for the past two years. The first symptom was that the systemwould not turn on or off. In other words if the heat was on, changing thetemperature sensors would not shut it off and vice versa. In thebeginning the problem was intermittent. I took it to a dealer who testedthe system and said it was functioning normally. About a year ago itfinally broke and the heat was on full all the time. I took it to anotherdealer that worked on it for over a month. They replaced the heatercontrol unit, the 3 blower motor resistors and the temperature sensor.Changing the blower motor resistors caused the front fans to shut off,but the engine fan and heat were still on full. The last thought was thatthere was a short in the wiring. After a month I took the car back,disconnected the rear heater blower hoping I could drive it without heatpouring into the car, but it did little. Upon driving the car home, itgot so hot in the car I turned the air conditioning on. Amazingly thiscaused the heat to shut off and when I reconnected the rear fan, it wasoff as well. I can now run the car with the heat and air conditioningoff. I have not touched the heater control knobs since then because I amafraid the system will come back on. Do you have any suggestions as towhat the problem may be? I want to get this fixed but I don't know how tofind a dealer or technician who understands the problem.

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